1. Field of the Invention
The present invention relates to high-numerical-aperture objective optical systems having a long, thin shape, and more particularly, relates to an immersion objective optical system suitable for insertion into an animal such as a mammal to carry out in vivo examination.
This application is based on Japanese Patent Application No. 2004-306154, the content of which is incorporated herein by reference.
2. Description of Related Art
In the related art, a dye or fluorescent marker is attached to specific molecules, tissue, cells, and so on and fluorescence microscopes, confocal laser-scanning microscopes, and the like are used to examine the behavior of the molecules in the cells and tissue of living organisms.
The behavior of molecules in a live individual mammalian organism, such as a mouse, may differ from that in cultured cells. Therefore, examination of biological tissue and the interior of cells is carried out while the individual organism is alive (in-vivo).
When examining the interior of a living organism, because the outer diameter of the objective lens in conventional microscopes is large, it is necessary to make a large incision in the living organism to carry out examination. Making a large incision in a living organism, however, is highly invasive, and therefore long-term examination is impossible.
In general, because endoscopes have small outer diameters, invasiveness to a living organism is low; however, because the magnification is low, it is insufficient for carrying out examination of the behavior of molecules inside biological tissue and cells.
A magnifying endoscope has high magnification, but because the numerical aperture (NA) at the object side is low, the resolution and brightness are insufficient.
On the other hand, objective optical systems having large numerical aperture, reduced outer diameter, and comparatively long overall length have also been disclosed (for example, see United States Patent Application No. 2004/0051957). With the objective optical system disclosed in this patent document 1, by making a small hole in a living organism and inserting the optical system through this hole, it is possible to examine the interior of the living organism with minimal invasiveness.
However, the objective optical system described in United States Patent Application No. 2004/0051957 does not sufficiently correct chromatic aberrations, and therefore, when carrying out white-light observation or fluorescence observation, the wavelengths of excitation light and fluorescence produced in the specimen differ, which results in the problem of low resolution.
In particular, in the case of fluorescence observation using a confocal optical system, not correcting the chromatic aberrations results in the problem of reduced brightness of the detected fluorescence.